1. Field of the Invention
The present invention relates generally to improved data storage technology, and in particular, but not exclusively, to a method and system for implementing discrete step stabilization of narrow-track, Anisotropic Magneto-Resistive (AMR) read sensors in magnetic media storage systems.
2. Background of the Invention
Tape drives are peripheral mass storage devices often used to archive data on tapes for later access. In certain applications, huge amounts of data are stored directly on magnetic tape for later retrieval and analysis. Tape drives are also used as random access devices in data storage applications where the cost of storage is more important than access time.
Data can be stored or written onto a magnetic media (tape or disk) by selectively magnetizing regions of the media with a write head. The magnetized regions of the media produce a magnetic field that can be detected and converted into an electrical signal by a read head. A common type of read head used for carrying out this conversion is an AMR read head.
More precisely, the operation of reading data from the magnetic media is performed by sensing the magnetic polarity transitions on the media as it is moved across a read head in a longitudinal direction. The magnetic transitions on the media present a varying magnetic field to a read transducer in the read head. The read transducer converts the magnetic field into an analog read signal that is delivered to a read channel for processing. The read channel converts this analog signal into one or more digital signals that are processed by a computer system.
In thin-film heads including a plurality of transducer elements, AMR sensors are often used to read information from the magnetic media, because of the increased sensitivity of the AMR sensors during read operations. During a read operation, an AMR sensor is held very near a disk or in contact with a tape, in order to sense the varying magnetic transitions on a particular track. A constant DC (bias) current is passed through the AMR sensor, and the sensed varying magnetic transitions produce a variable voltage across the sensor due to its varying resistance. This variable voltage signal is the read analog signal, which is then processed and converted to digital form.
A common goal in the information storage industry is to magnetically stabilize AMR read elements so that the generated electrical signals are linear. This goal is frequently accomplished by controlling the boundary or end magnetic domains in the read sensors involved. In the past, this boundary magnetic control was provided by permanent magnets or magnetic exchange tabs attached to the ends of the sensors. However, the greater the width of the track containing the stored data, the less effective boundary magnetic control was at the center of the read sensor.
One technique used to overcome this limitation has been to form a periodic perturbation (grating structure) which creates a periodic magnetic charge that stabilizes the middle region of the sensor. However, the resulting periodic perturbation can interfere with the magnetic field of the permanent magnet(s). This interference problem is exacerbated as the read heads are made smaller.
An improved magnetic stabilization technique for MR read heads is described and claimed in related U.S. Pat. No. 7,139,156 entitled “NON-PENETRATION OF PERIODIC STRUCTURE TO PM”. This technique limits the undulations of the periodic grating structure used for magnetic stabilization of an MR read sensor to regions that are not directly adjacent to the permanent magnets attached at either end of the sensor. This technique allows the permanent magnets to stabilize the magnetization near the ends of the sensor, and also allows the periodic structure to stabilize the magnetization in the middle region of the sensor without perturbing the permanent magnets.
Nevertheless, a significant problem that has arisen is that read sensors are being made narrower while the pitch of the periodic structures is constrained. For example, in one of the narrowest track sensors currently being produced, only a single stabilizer centered on the sensor is used. Consequently, it is no longer tenable to regard such a structure as periodic.
In actual fact the parts of a stabilizer that influence magnetic behavior are the steps located beneath the sensor (e.g., depressions precisely milled typically in an Aluminum Oxide/Alumina (Al2O3) underlayer directly beneath the sensor). Therefore, it is desirable to have an improved method and system for implementing discrete step stabilization of AMR read sensors including, for example, narrow-track, AMR read sensors.